Process for the production of alumina



Patented lit/lay 2Q, 392d.

stage BIRGER FJELD HALVORSEN, OF CHRISTIANIA, NORWAY, ASSIGNOR T0 NORSK HYDRO- ELEKTB ISK KVAELSTOFAKTIESELSKAB, OF CERISTIANIA, NORWAY.

EBOCESS FOR THE PRODUCTION OF ALUMINA:

No Drawing.

To all whom it may cmwem:

Be it known that I, Bmona FJELD HAL- voRsnN, a citizen of the Kingdom of Norway, residing at Oscarsgate 71, Christiania, Norway; have invented certain new and usein! Improvements in Processes for the Pro duction of Alumina, of which the following contain other bases various mixtures of n1- trates, for instance, a mixture containing in: trate ofaluminum and nitrate potassium are obtained by c stallization ofthe solutions referred to. arious methods may be employed for forming alumina and separating it from the nitrates of the other metals of such mixtures of nitrates.

For instance, in the case of a mixture of nitrate of aluminum and nitrate of potassium, the alumina can be separated by treating an aqueous solution of the mixture with carbonate of potassium, whereby alumina and nitrate of potassium areobtained. In the case of compositions containing nitrate of sodium, soda can be used whereby nitrate of sodium is obtained. The alumina can also be separated by means of ammonia whereby alumina and a mixture of nitrates consisting. of nitrate of ammonium and the nitrates of alkali metals are obtained.

The drawbacks connected with this process are, however. that the alumina is obtained in a gelatinous state and is diiiicult to Work with.

Another process is to separate nitrate of ammonium by means of heating. On performing this process it will be noticed that the nitrate mixture melts at a comparatively low temperature. Gradually as the separation progresses. the solution gets stickier 95nd stickier. till at last it becomes quite iolid. Theincreased .viscidity of the solu" ion and the separation of the solid stuffs Application filed March 2, 1932. Serial No 540,581.

causes the mass to stick to the walls which are heated rather strongly. This hinders the heat supply and the apparatus stops up little by little. The diiliculties this causes are sogreat that itis hard to construct an ap aratus suited to the purpose.

ccording to the present invention the mentioned difficulties can be avoided by dccomposing the nitrate of aluminum in a molten mixture of the nitrates so that the alumina produced by the decomposition of the nitrate of aluminum floats in the molten mixture. molten mixture is to add to the mixture of nitrates a nitrate of an alkali metal and preferably the nitrate of the same alkali metal as that accompanying the nitrate of aluminum in the mixture of nitrates under The best way to produce the treatment. If however it is desired to produce fertilizers as a by product of the alumina product various nitrates can be used, depen ing upon the composition of the fertilizer salt desired. When a mixture of nitrates is used it will lower the melting point of the molten mixture and thus make it easier to keep it liquid when draining the molten mixture together with the alumina.

The process of separation takes place at such a low temperature that the se arated alumina does not react with the alka i metal nitrates to" give aluminates. After the reaction is at an end the finished product is drained from the apparatus and it can either betreated disoontinuously orv the molten mixture can flow from an apparatus that is continually in operation to those apparatus where the alumina is to be separated from the undecomposed nitrates.

The separation can be effected by extraction in the usual way after the smelted solution has stifi'ened. But the molten mix paratus. 

